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Add answers for lab3 part A

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Danila Fedorin 2019-05-06 22:22:13 -07:00
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1. Some interrupts receive a different "shape" of stack frame - the kernel pushes
an error code for some, but not for the others. We thus need individual handlers
that would make sure that what we have on the stack is consistent, and
then call one centralized function for that. The handlers additionally
are able to pass in a trap number to that centrallized function. This way, a lot
of code can be re-used.
Conceptually, each trap has a different semantic meaning. Thus, it makes no sense
to perform the same action for both traps - they don't mean the same thing.
2. The general protection fault occurs when a process can access memory, but not do something else with it. We do not want page faults to be trigger-able by users (this is the case for many other traps). Thus, when the user tries to invoke int 14,
it's not allowed to execute it from userspace, so it is thrown a general protection fault, which it then prints.